It is concluded that eucalypt planting can be vastly expanded
in Bangladesh without a serious impact on the environment and that environmental
confusions of the use of eucalypts can be minimised in stand management with
appropriate techniques. Eucalypts are favoured due to their high productive
potential, and found superior to other species. Some 456,000 ha is assessed as
suitable for eucalypt planting which on short rotations can produce 6-8 times
more stem wood than present forest crops; highway and feeder road planting area
are available, equivalent to 988,000 ha, and could produce energy roughly 20
times more than present crude oil imports ($200 million/yr). No negative
reaction to eucalypt planting were noted by village people, a review showed 80%
in favour of short rotation species with emphasis on cash crop objectives of
fuel production. It is considered that further extension and explanation of
[land] resource allocation and management inputs would increase choice of
eucalypts because the crown structure is suitable for combination with
agricultural crops. Problems of allelopathy, nutrient depletion and water use
are considered together with appropriate management techniques. The lack of in
country improved seed/plant sources is noted as is the need to develop markets
and uses to increase the economic importance of eucalypt wood
production.

Though eucalypts have become important industrial species in
many countries, debate still remains about their effect on the environment;
objection to large scale planting is very intense in India (Shiva and
Bandyopadhyay, 1983; Karanth and Singh, 1983). However, the current expansion
rate of eucalypt around the world shows not all countries embarking in large
scale plantations are convinced by concerns raised in India.

This controversy has resulted in confusion about the
suitability of eucalypt plantations in Bangladesh. Research results suggest that
some provenances of several species of the genus are suitable for the country in
terms of growth and site adaptability. As a result the country has undertaken a
large scale eucalypt planting program and to date 6,500 ha have been brought
under plantations to supply domestic fuelwood. No specific research project has
yet been under-taken to verify objections under Bangladesh conditions. In some
cases, it is assumed that the effects in Bangladesh are the same as those in
India; as a result, a confused/negative attitude towards eucalypt planting has
developed among policy makers, politicians and elites.

However the mass of rural people, who plant eucalypt on their
homesteads have not shown any negative reaction to these environmental whims.
These people participate in tree planting in small rural woodlots, agroforests
and marginal land rural areas. An early return of a handsome volume of wood is
very important to them. They are in crucial need of fuelwood, poles and posts
for domestic uses. So a sharp divergence of opinion exists between different
groups of people in society.

In the 1930s Eucalyptus citriodora Hood was
haphazardly introduced into eastern Bangladesh by tea estates as an ornamental
(Davidson and Das, 1985; Zabala, 1990). The species was spread widely by
botanists, foresters and gardeners but no plantation was established. First
interest on other species of eucalypt was recorded in 1963 when germination
tests of three species E. citriodora, E. tereticornis and E.
botryoides were made in the silvicultural research stations at Mymensingh
and Chittagong (Davidson and Das, 1985). From then on until 1984 about 37
species were introduced and tried (Islam and Neven, 1989). After five years of
experimentation, the Bangladesh Forest Research Institute in Chittagong arrived
at the conclusion that E. camaldulensis Dehnh, E. tereticornis, E.
brassiana S.T. Blake, could be profitably grown in the soil and climatic
conditions of Bangladesh (Das, 1984). Since then small scale planting on
degraded lands and roadside have been initiated. Initially spacing was 3m x 3m,
later reduced to 1m x 1m to maximize production. Actually eucalypt were
introduced in this subcontinent much earlier than Bangladesh, for instance, in
1867 in Pakistan, in 1919 in India (Chaturvedi, 1983). At present eucalypt
planting around the world extends to about 80 countries and another 50 countries
are in trial phases.

NEED FOR EUCALYPTS

Bangladesh, with more than 110 million population over an area
of 14.3 million (mil.) ha is highly populated, 764 persons per square km. About
83% of the total population live in rural areas. The country is mostly composed
of flood plains except some hilly areas along the eastern and north eastern
boundaries and upland terraces on the central and north western regions. Of the
total land area 0.93 mil. ha are waterways, 8.5 mil. ha cropped area, 2.67 mil.
ha uncultivated land and 2.2 mil. ha declared Forest Land. However, only 0.93
mil. ha (6.5%) is under tree cover, some 40% of the Government controlled
forests (UNDP/FAO, Global Environmental Monitoring System 1983-84; Huq and
Banik, 1992). The remaining 60% Government forest includes denuded grasslands,
scrub and encroached lands. The forests are unevenly distributed and of low
productivity types because of their heterogeneous character.

The regional disparities of forest resources and population
distribution reflect the highly populated areas, central and northern regions,
have practically no natural forest or plantations, while least populated areas,
eastern and south western, contain almost all the natural forests and
plantations (Figure 1).

Figure 1. Population distribution and regional
disparities in respect of forest resources

Regions

Population (%)

Natural Forest (%)

Village Graves (%)

Plantation (%)

Region1:

25

1

24

0

Rangpur, Dinajpur, Bogra, Rajshahi, and Pabna

Region2:

24

7

18

2

Dhaka, Mymensingh and Tangail

Region 3:

13

0

15

0

Kustia, Jessore and Faridpur

Region 4:

14

6

4

10

Sylhet and Comilla

Region 5:

5

42

7

0

Khulna

Region 6:

12

3

23

14

Barisal, Patuakhali and Noakhali

Region 7:

6

16

9

43

Chittagong

Region 8:

1

25

0

31

Chittagong Hill Tracts

Total

100

100

100

100

Source: Davidson (1984); Huq and Banik
(1992)

Figure 1 highlights the problem of mal-distribution of public
forests on one hand, and the importance of highly productive people oriented
forest activities in particular areas, on the other. The possibility of
horizontal expansion of forestry activities is limited. A comparative statement
of change of land use pattern from 1973 to 1987 (Figure 2) indicates the
potential of horizontal expansion of forests.

Figure 2. Comparison of land utilization (x 1000 ha) in
Bangladesh from 1973 to 1987

Land use type

Area 1973

% total of

Area 1987

% of total

Cultivated cropland

8,438

59.1

8,857

59.8

Forest

2,230

15.6

1,988

13.4

Cultivable

274

1.9

266

1.8

Current fallow

680

4.8

400

2.7

Not available for cultivation

2,661

18.6

3,296

22.3

Total

14,283

100.0

14,802

100.0

Source: FMP, 1992 (landuse)

The homestead village woodlots currently supply 53% of annual
consumption of timber, fuelwood and bamboo in Bangladesh (FMP, 1992). Dependence
for this produce on the village woodlots is almost 100% in non forested areas
(Figure 1). As a result, a substantial decline in tree cover is also common in
rural areas.

Though there are several causes of forest decline, over
exploitation to meet industrial and domestic demand is the most important. A
large tract of forest land, Unclassed State Forests (USF) of Chittagong Hill
Tracts, has become barren and degraded due to shifting cultivation and over
exploitation. Reserve Forests of Rangkheong, Chittagong were depleted by 61%
between the years 1963 to 1983 (Chowdhury and Hossain, 1989) promoting further
deterioration of the environment. As eucalypts have adaptation potential to
degraded areas and grow faster than many native species, the country has been
raising eucalypt plantations largely on degraded sites.

PRESENT STATUS OF EUCALYPTS

Three species, E. camaldulensis, E. tereticornis and
E. brassiana have proved superior to over 30 others tried in the country
(Davidson, 1985). With these species Petford, Mt. Garnet and Coen provenances
respectively are the best ones. After 5 years of growth, mean annual increment
per ha ranged from 11.7 to 95.6 m3 for Petford, 4.9 to 66.6
m3 for Mt. Garnet and 7.3 to 34.2 m3 for Coen (Figure
3).

Figure 3. MAI in m3/ha/yr of three superior
provenances at different research stations at the age of 5 years

Locations

E. camaldulensis (Petford)

E. tereticornis (Mt. Garnet)

E. brassiana (Coen)

Lowachara

17.1

4.9

10.3

Charaljani

95.6

66.6

34.2

Charkhai

20.7

12.2

16.3

Hathazari

28.9

12.6

23.9

Keochia

11.7

-

7.3

Source: Davidson et al (1985)

The Petford provenance of E. camaldulensis has been
planted widely in Bangladesh to supply fuelwood at a rotation of 6 years and,
poles and posts at a rotation age of 12-18 years. Block plantations with
eucalypt currently cover an area of 6,500 ha (Figure 5). These plantations were
established mainly on accessible lands of three hill Districts of Chittagong,
Chittagong Hill Tracts and Sylhet in the east. Seed for plantations are
collected from provenance and growth trials of the Bangladesh Forest Research
Institute.

Keen interest is shown in raising eucalypts along roadsides,
homestead agroforests and rural marginal lands (Figure 4). The Forest
Department, NGOs and rural population are mainly involved in these plantings.
About 10,000 ha of land are in agroforests, mostly eucalypt and acacias (Figure
4). The proportion of eucalypts in these plantings is unknown but it may be
assumed to be not less than 60% of the planted area.

In the hill Districts of Bangladesh of Chittagong, Coxs Bazar
and Sylhet, where most of the forest areas are located, some eucalypt
plantations have been established; areas established from 1985-92 are shown in
Figure 5.

Source: Latif (1993): long rotation over 30 years,
short rotation 12-18 years and fuel wood rotation is 6 years.

PROSPECTS FOR EXPANSION

Eucalypt planting objectives are restricted to production of
fuelwood, poles and posts only. The species have potential for the production of
raw materials for industries, pulp wood industries; plenty of land is still
available for tree planting.

The central and the NW regions contain 50,181 ha of tree cover
though the total notified forest areas in these regions are estimated as 113,654
ha (Chowdhury, 1993). These forest areas are scattered, small patches and they
are under heavy exploitation pressure. As a result the areas are ecologically
fragile and need restocking and proper management to balance extraction with
planting. Planting on these areas alone will not lessen the pressure on natural
tree cover; planting in marginal lands is also important and some 31,573 km of
road and highways are still available for strip plantations in 61 non forested
Districts in Bangladesh (Figure 6).

These marginal lands are suitable for eucalypt planting.
Marginal lands in some cases can be planted in multiple rows whereas feeder
roads cannot be planted by more than one row. Karim (1991) has calculated that
Bangladesh can establish energy plantings along highway and feeder roads which
are equivalent to 988,000 ha and thereby produce energy which is roughly 20
times more than crude oil imported annually. Moreover, 140,000 ha of land are
available for energy plantations in the unclassed state forests of the south
east

Figure 6. Marginal lands available for
plantation

Types of land

Length (km)

Road length along Highways (R & HD)

12,834

Road length along Railways

2,721

Road length along Embankment and Irrigation Canal
(BWDB)

10,028

Road length along Feeder Road

5,990

Total

31,573

Source: Chowdhury (1993)

Richards and Hassan (1989) studied the suitability of
Bangladesh soil for growing eucalypt on land capability classes. About 456,000
ha were found suitable for eucalypt (Figure 7). These areas could produce 3-4
times more biomass and 6-8 times more stem wood on short rotations with eucalypt
than the present forest crops (Munshi, 1986). Chowdhury (1993) studied growth
potential of E. camaldulensis, Acacia auriculiformis and A.
mangium by a site index method of growth and showed eucalypt better than
acacias (Figure 8).

Figure 7. District wise area of land in 1,000 ha suitable
for raising eucalypts

Districts

Very highly suitable

Highly suitable

Thakurgaon

56.3

48.7

Rangpur

44.5

20.2

Cox's Bazar

22.2

53.5

Joydevpur

13.4

74.8

Khulna

6.4

6.0

Rangamati

5.3

13.7

Comilla

3.5

3.6

Sylhet

1.5

50.7

Pubna

0.1

32.0

Subtotal

153.2

303.2

Source: Richards and Hassan (1989

Figure 8. Average site index of main species planted in
woodlot and agroforests

The future of eucalypts in Bangladesh depends on their
acceptability in society among different groups of people. To indicate the
degree of acceptability, it is relevant to understand how people react with
participatory forestry practices specially in woodlot and agroforestry
plantations where eucalypts are the major components of the systems.
Peoples participation is so far, encouraging in such plantation activity.
The average participants in woodlot and agroforestry plantations are about one
family per ha and peoples participation is increasing day by day (Figure
9).

Figure 9. Statement of number of participants in
plantations of the years from 1988 to 1992

Forest Divisions

Plantation Type

1988

1989

1990

1991

1992

Total

Dhaka

Woodlot

-

-

107

123

240

470

Agroforest

-

-

143

54

32

229

Tangail

Woodlot

7

53

626

1,096

877

2,659

Agroforest

-

-

127

177

161

465

Mymensing

Woodlot

27

92

309

651

791

1,870

Agroforest

-

-

36

34

103

173

Comilla

Woodlot

-

-

-

42

-

42

Agroforest

-

-

33

9

-

42

Dinajpur

Woodlot

15

127

268

318

343

1,071

Agroforest

80

45

149

132

161

567

Rangpur

Woodlot

-

-

2

85

89

176

Agroforest

28

10

82

33

251

404

Rajshahi

Woodlot

-

-

209

167

428

804

Agroforest

-

-

-

-

64

64

Total

Woodlot

49

272

1,521

2,482

2,768

7,093

Agroforest

108

55

570

439

772

1,944

Source: TANDP, Bana Bhavan, Dhaka

Social surveys can also be a indicator of social acceptance of
eucalypts. Chowdhury (1993) interviewed people living in and near the forest and
plantation areas to understand their preference in choosing species. Among the
interviewee, 80% favoured short rotation species, 15% favoured combination of
short and medium rotation species, whereas less than 2% respondents favoured
long rotation species; the rest did not have any choice or they did not
understand about the choice. However, none mentioned fuelwood as the first
priority but the majority advocated cash returns. It was found the majority
prefer E. camaldulensis to A. auriculiformis.

The Swiss Development Corporation has been conducting research
from 1986 on tree growing in the khet (abandoned area) and has the
experience of farmers favouring E. camaldulensis. In the D & D
(Diagnosis and Design) survey, conducted by BARI, BRAC and ICRAF in 1991, it was
reported that the tendency was to give lowest priority to trees in terms of
resource allocation and management inputs, as farmers have little knowledge of
production potential and management of trees. However, if they are motivated and
provided with technology, they would prefer eucalypts as their first priority
species in agroforestry because of its better crown architecture suitable to
their agricultural crops.

A third approach could be users preference. With the
increase in alternative uses of eucalypt, acceptability will increase. For
instance, cottage industry where about 75% of total industrial labour forces are
employed (Chowdhury, 1993), depends on local timber species, bamboo, canes, and
murta. Exotic species like acacias and eucalypt are yet to be exploited in this
sector. Though eucalypt can be used in many secondary timber based industries as
pulp, veneer, hardboard, particle board, matches and furniture it are not used
for such purposes in Bangladesh. If the uses of eucalypt are fully explored, and
management techniques to increase production rate per unit land area are
adopted, their acceptability will increase further in society.

POLICY ISSUES ON EUCALYPTS

There has been a lot of interest in the forestry sector to
cover the barren and marginal lands with plantations of rapid growing species. A
Thana Afforestation and Nursery Development Project has aimed at the
establishment of short rotation plantations over an area of more than 20,000 ha
(Figure 10). In addition there is a target to train about 75,157 individuals and
the development of 91 forest extension nurseries to promote extension activities
in the rural areas.

This year arrangements are made to plant about 85 million
seedlings and the Government has instructed nurseries to raise 100 million (15
million excess) seedlings so mortality filling can be made with comparatively
older seedlings. The Prime Minister has urged the people to plant and grow at
least one tree for each individual in their marginal land. So far 22 large NGO
organizations have planted 12.5 million seedlings. At present some 676 numbers
of NGOs and their 125,000 workers are engaged in plantation activities. There
are poor statistics available concerning the species composition of those
activities.

From field observation, my general impression is that most of
the NGO people are engaged in short rotation crops with exotic fuelwood species
with an emphasis on eucalypts. In the last few years Government organizations
have also preferred fuelwood crops. This year the Government is especially
giving advice to plant more fruit trees. Probably poor performance (maybe due to
an inbreeding problem) of some eucalypt plantations in the hill areas of
Chittagong Forest Division have created some confusion. It is possible a
negative attitude may have developed within the Government concerning eucalypts.
The minutes of a Government meeting on plantation programs in January 1993
proposed action to discourage eucalypt plantings but no specific reason was
outlined. Perhaps environmental confusion, resulting from eucalypt controversies
in some countries may have led the Government to develop this attitude. These
eucalypt environmental issues have yet to be justified by indigenous
study.

CRITICISM OF EUCALYPTS

Eucalypt planting is a controversial issue in some countries
where it has been planted extensively. Critics assert that: i) it has
deleterious effect on the hydrological balance; ii) it depletes the soil
nutrients; iii) it has an allelopathic effect leading to inhibition of growth of
other plants; and iv) it has a deleterious effect on native animals. This may be
disputed by the reasoning that it is highly unlikely that a genus with
outstanding evolutionary adaptation to infertile soils and a dry climate of
Australia will use excessive water and nutrients.

Eucalypt as a single entity failed to take account of the
great climatic and edaphic diversity of the Australian continent. There are more
than 600 eucalypt species differing in inherent growth rates, environmental
adaptation to low nutrient soils, and dry climates. Within the Australian
forests site factors exert a strong control on species composition, stand
structure, leaf area index and productivity. As each unit of forest in Australia
is in balance with the particular characteristics of the site, the eucalypts are
not making excessive demands on the resources of that site.

Where a eucalypt is planted in countries other than Australia,
it is removed from its regulated environmental context, and the checks and
balances imposed by site no longer apply. For example, E. camaldulensis
occurs naturally as a woodland in dry areas over most of the Australian
continent where the rate of water use is hardly an issue in the Australian
circumstances (Florence, 1992), it could become an issue where it is established
elsewhere as a forest on moderately fertile soil with good rooting depth and
access to a water table.

ATTRIBUTES OF INTRODUCED EUCALYPTS

It is important to understand the attributes of eucalypts
planted in Bangladesh to understand their environmental consequences. The most
outstanding eucalypts introduced are E. tereticornis and E.
camaldulensis. These species, including others introduced elsewhere as
exotics, as E. grandis and E. urophylla in the Indo-Malaya region,
tend to have a number of characteristics in common:

(a) They belong predominantly to the subgenus
Symphyomyrtus - individual members of which may be characterized by a wider
environmental tolerance than members of other subgenera.

(b) They are the more successful species capable of responding
more positively to better soil conditions - particularly higher soil
fertility.

(c) They are capable of rapid root development, particularly
in depth. This may be a general attribute of eucalypts growing, or capable of
growing, away from moist regions.

(d) The species usually reach early and strong peaks in
current annual volume increment (CAI). This peak may be as early as 4 years in
E. tereticornis, 6-7 years in E. grandis and 12-15 years in E.
globulus. By the time the peak is reached wood volume production on high
quality sites may be in the range of 24 m3/ha/yr for E.
tereticornis to 50 m3/ha/yr for E. globulus (Florence,
1992).

The controversial effects of eucalypt on environment should be
seen with respect to its attributes, and high productivity within a short
duration.

ALLELOPATHY AND EUCALYPTS

It is widely held in some countries, notably India, that
eucalypts are strongly allelopathic; that they produce foliar and root exudates
directly toxic to other plants. This may not be true in all cases. It is more
likely that the effect of eucalypt on understory plants or adjacent crops are
the result of the very great capacity of eucalypts to compete for short supply
soil resources (nutrients and water). Where soil resources are not in short
supply the understory vegetation may be maintained under a vigorous tree
canopy.

In India Dabral et al (1987) found an undergrowth
vegetation of Lantana spp., Murraya koenigii, Carissa karonda,
Jasminum officinale, Mallotus philippensis and Syzygium cumini under
16 year old Eucalyptushybrid plantation, at spacing 2m x 2m, at
an experimental site near Dehra Dun Forest Research Station. In our forest
conditions undergrowth develops, especially if spacing is more than 1m (Bhuiyan,
1986). I have observed undergrowth under eucalypt plantings at 1.8m x 1.8m
spacing but the diversity is less than of native forest types. The composition
observed could have been disturbed by weeding, ground fire and shrub collection
of local people and a confirmation study of the diversity of undergrowth needs
to be made under suitably undisturbed eucalypt plantation.

Lisa and Michelsen (1993) reported in Ethiopia that eucalypt
leaf exudates have some inhibitory effect on germination, and on reduction of
shoot dry weight of four crops tested; they state an allelopathic potential
rating from lower to higher as Cupressus lusitanica < E. globulus < E.
saligna < E. camaldulensis. This type of exudate allelopathy may be
controlled by management techniques under rainfall conditions of
Bangladesh.

NUTRIENT DEPLETION BY EUCALYPTS

During the rapid biomass accumulation phase, fast growing
eucalypts will accumulate a store of nutrients in the phloem and sapwood (7-10
years of growth). This nutrient is withdrawn very efficiently from the cells at
heartwood formation and maintained in a mobile phloem - sapwood pool (Banks,
1992). As there is a very low residual concentration of nutrients in the
heartwood, the mature stand in the natural environment manages on a much smaller
biomass nutrient pool than in a forest of comparable productivity elsewhere. A
large tree will have a thin shell of relatively nutrient rich active tissue
surrounding an inert bole wood mass. The tree can be felled and removed at low
nutrient cost to the site, i.e. a small amount of nutrient is exported per unit
weight of wood.

Alternatively where the stand is grown in well stocked
plantations and harvested on short rotations (e.g. 6-10 years), there may be a
substantial nutrient cost to the site. Pande et al (1987) reported
harvesting of utilizable biomass (bole, bark and branch) at age 10 years in
Kerala Forest Division, India, results in the removal of 52% nitrogen (N), 70%
phosphorus (P), 66% potassium (K), 78% calcium (Ca), and 67% magnesium (Mg); the
removal of N, P, K, Ca and Mg will be 42%, 55%, 54%, 61% and 56% respectively in
the Madhalli Afforestation Center at the age of 7 years. A major depletion of
site nutrient is caused by early removal of the crop, rather than to deleterious
effect of eucalypt plantations. The site nutrient depletion by early biomass
removal may also vary from site to site and species to species at a particular
age of harvest. Yet, scientific opinion is, that such cost may still be no
greater than what of other fast growing tree species.

The nutrient accumulation is generally greater in species with
a comparatively larger crown biomass relative to stem size. The ranges of
nutrient accumulation in E. camaldulensis was established by Hopmans
et al (1990) (Figure 11). A considerable amount of N accumulated in the
leaves and twigs of eucalypt can be left in the forest environment, and would
compensate for the loss to some extent but in case of other macro nutrients some
corrective measures may have to be taken. This is very important, especially in
the case of eucalypts, because nutrient content in the litter of eucalypt is
lower than other species as they usually absorb nutrients before the shedding of
litter (Banks, 1992). Sing et al (1989) state that the litter of
Populus deltoides contains 1.3 times more N and 1.5 times P and K than of
E. hybrid. Additions of N, P and K to the soil through litter
decomposition was respectively 36.6%, 91.6% and 69.9% more in P.
deltoides than the E. hybrid. Moreover, litter fall was 5 kg per tree
per year for P. deltoides whereas for E. hybrid it was only 1.5
kg. Bahuguna (1991) reported that litter decomposition is faster under eucalypt
than under Sal. In Bangladesh the loss of soil nutrient may be more
severe as the litter layer and the leftover debris on the forest floor are
regularly harvested. If we consider these human factors and the early harvesting
of eucalypt, the depletion of soil nutrients by the deleterious effects of
eucalypts is not an established fact under the social conditions of
Bangladesh.

Figure 11. Range of nutrient content in gm/m2
of leaf area depending on the crown size

Nutrient type

Range of nutrient content

Nitrogen

24.0 - 41.0

Phosphorus

2.6 - 5.9

Potassium

12.0 - 27.0

Calcium

7.0 - 52.0

Magnesium

3.1 - 7.9

Sodium

0.5 - 9.2

Source: Hopmans et al (1990)

WATER USE BY EUCALYPTS

Claims are made that eucalypts use excessive amounts of ground
water by developing a deep root system. In dry areas, though eucalypts develop
long deep tap root in moist areas, they mostly develop fibrous roots (Zimmer and
Grose, 1958). Dabral et al (1987) observed that the fibrous root of
eucalypts extend up to 18 m within a soil depth of 30 to 60 cm in moist areas.
When moisture content varies at different localities of a site, eucalypts may
try to maintain growth by extending root systems in drier areas. An observation
on height growth of E. camaldulensis at top hill and valley shows that
first year growth was significantly different from the top to the valley but
from the second year height growth was not significantly different (Figure 12).
This adjustment could have taken place by differential expansion of the root
system by eucalypts for enough moisture. A supportive statement to this effect
is noted by Pal and Raturi (1991). They studied the dry biomass production of
E. hybrid in a semiarid environment under rainfed condition. The stand
was divided into three classes according to the height growth of the species and
found that at the age of three, the lowest class produced 31.8% root biomass
whereas the highest class and the middle class root biomass was 21.0% and 26.7%
of the total biomass respectively. The higher root development of suppressed
trees may be to capture more moisture from the soil to maintain the
physiological need and hence growth potential to compete with the dominant
trees. However, the following points can be made against the statement of
excessive water use:

(a) Florence (1992) mentions that in a regrowth
forest of E. regnans, a strong early peak in CAI (current annual
increment) water yield declined for some 25 years before beginning to rise
again. The pattern is closely related to the pattern of volume production for
this species, that is, a peak in CAI occurs around 20 years.

(b) Some eucalypts which are widely planted as exotics, have
even faster early growth rates than E. regnans, and a strong early peak
in CAI, e.g. E. tereticornis, E. grandis, and E. camaldulensis.
Where these species are planted on high quality sites with access to a good
soil water resource, high rates of water use might be anticipated at an early
age. This is expressed, for example in the rapid decline in stream flow as early
as 6 years on an E. grandis catchment in South Africa (Florence,
1992).

(c) It is possible that where one of the more opportunistic of
the faster growing eucalypts (e.g. E. camaldulensis) has access to a
substantial water resource (e.g. a water table at 1 to 2 m), and where there is
a prolonged dry period with high vapour pressure deficits, large amounts of
water may be transpired. In this case, water use efficiency may be low. This may
explain why E. camaldulensis has sometimes been planted to help drain or
control swamps (Florence, 1992).

Figure 12. Height variation of eucalypt at different age
between valley and hill top in Chittagong. Significance tested at p =
0.05 level.

Year of plantation

Age (yr.)

Valley ht (m)

Tophill ht (m)

t-calculated

t-tabulated

1991

1

5.78

2.90

16.000

2.024

1990

2

7.91

7.27

0.380

2.204

1989

3

9.91

8.59

1.168

2.024

1988

4

12.58

10.47

1.320

2.204

1987

5

14.86

13.82

0.810

2.024

1986

6

17.70

17.40

0.180

2.024

1985

7

20.20

20.00

1.360

2.024

1983

9

23.30

22.86

0.190

2.024

1981

11

23.46

22.76

0.240

2.024

1980

12

24.50

23.68

1.607

2.024

Source: Anon (1992)

Alternatively where the same species does not have access to a
substantial water resource, moderate level of wood production may still be
obtained under rainfed conditions. In this case other attributes of the species
may be important, for example, the capacity to maximize access to water supply
through an extensive root system, and to tolerate relatively high levels of
water stress. Again the species may not extract soil water to the same level of
potential as other species, thus helping to maintain some contact between the
root system and soil water under dry conditions. In these manner, site
attributes, wood production and water use may be closely related.

Thus, while a species reputation for high water use may be
justified under some conditions, it cannot be justified in others. It is
difficult to accept in our condition where the plantation depends entirely on
rainfall infiltration to the soil, that eucalypts should not be planted because
of excessive water consumption. Indeed, eucalypts may not survive at all unless
it can open stomata and transpire water daily. This means that eucalypts cannot
dry out soil entirely but do it proportionately to the availability of moisture.
A supportive statement may be mentioned from Lima et al (1990) who
reported from the cerrado region of Brazil, where rainfall is usually 1,100 to
1,150 mm per year that establishment of forest plantation with the eucalypt and
pines will not adversely affect the soil water regime. In Bangladesh annual
rainfall ranges to about 3,000 mm and hence water use by eucalypt may not be a
problem.

MANAGEMENT STRATEGY

Appropriate management techniques could improve the social and
environmental consequences of the use of eucalypts in Bangladesh. For example,
thinning a stand will reduce water use and increase stream flow at least
temporarily. Thinning may remove those trees which are more inefficient user of
water (e.g. transpiring but producing little wood). Indeed, in the jarrah forest
of Western Australia, a heavy thinning to retain the better trees resulted in
both increased wood production and increased stream flow (Florence, 1992). In
our condition one option might be to thin early for fire wood production and
maintain the residual trees over a longer rotation of pulpwood production. For
fast growing eucalypts, it is surprising how small the stocking may be, yet,
produce maximum site volume production.

Eastham (1990) studied the relationship between stem density
and water use efficiency with 2,150, 304 and 82 stems per ha to relate
transpiration with biomass production. Tree density modified biomass production
and water use of trees, with both being consistently lower at the higher
densities throughout the study. Values varied both with season and with year.
This means that selection of a suitable stem density in a stand may help in
water management for efficient use.

Crop improvement may be another strategy to minimize the
consequences. In Bangladesh, though there were some provenance trials for
selection, no seed orchard has been established. Local and rural nurseries use
seed from provenance trial plots and distribute these for planting. As a result
projected yields from the planting are not available in the field from these
inbred seedlings, and lead to social disparities. A seed orchard designed to
hybrid production, and clonal propagation from selections may improve the yield
and protect land race formation.

The hybrids and clones can be planted in small patches with
native species forming a mosaic of mixed stands may solve the problems of
allelopathy and wildlife diversity, while at the same time, productivity can be
maintained. Appropriate research should be taken on this line.

CONCLUSIONS

Eucalypts have been introduced into Bangladesh for a long
time. But within a short period, a large degraded forest area has been planted
with eucalypt. A lot of interest is shown in eucalypt planting in: agroforestry,
marginal land afforestation and homestead forestry. There is some confusion
within elite circles about eucalypts but this is not apparent in the rural
people.

One of the reasons of wide acceptance of eucalypt is its high
productivity. This productivity potential should be maintained through adopting
appropriate technology to uphold the interest of rural mass. However the full
use of eucalypt has not been tapped; introduction of alternative uses will
increase the economic importance of the species.

Environmental confusion on eucalypts can be minimized by stand
management and crop mixing. Considerations of environmental factors should have
priority in crop rotations, whereas productivity should be maintained by
improved technology. This review stresses that selection of appropriate
provenances for specific sites is important for efficient output.

Horizontal and vertical expansion of eucalypt planting is
possible in Bangladesh without a serious impact on the environment. The economic
importance of the species can also be extended, support is extended to research
to be undertaken to promote eucalypt planting in Bangladesh.

FUTURE RESEARCH NEEDS

In Bangladesh eucalypt research programs were limited to
provenance and elimination trials. Priority should be given to research on the
following characteristics of eucalypts:

Eucalypt and other
species interaction, particularly for species in mixed plantations;

Eucalypt and undergrowth
patterns under the monsoon climate of Bangladesh;

Impact of eucalypt on wildlife
habitat, particularly in mixed plantations;

Interception of precipitation;
soil moisture relationship; comparative studies of native species and
eucalypts;

Natural and chemical exudates
of stem flow and infiltrates from eucalypts;

Effect on soil chemicals and
soil micro and macro fauna, due to litter and exudates;

Genetic improvement study with
efficient water use management objectives; and

Stand management strategy for
maximizing benefits.

Studies related to these fields are important before talking
about eucalypts. Based on derived information we may expect that the rotation,
intensity, scale and spacing of plantations, be adjusted for harvesting the best
benefits - in terms of yield and of the environment.